1. FIELD OF THE INVENTION
The present invention relates to data sensing and processing devices for SCUBA divers and more particularly to a portable underwater computer for a SCUBA diver using a tank of compressed air wherein the instrument measures several variables and provides integrated information to the diver numerically and graphically to permit the diver to make a variable depth dive with the longest time underwater allowing for a no-decompression ascent.
2. DESCRIPTION OF THE PRIOR ART
One of the primary problems for an underwater diver to avoid is "decompression sickness" commonly known as the "bends". This condition results from tissue saturation with the inert gas components of air (basically nitrogen). It has been fully studied, and procedures for avoiding it have been set forth in the writings by Boycott, Damant, and Haldane (1908), further developed by Behnke (1942), Hempelman (1952), Roshbash (1954), and Workman (1965). The principal method now used to prevent the condition after saturation occurs is a series of decompression pauses during the diver's resurfacing ascent. This allows time for out-gassing of the excess inert gases which have accumulated in the body issues. Schedules of these resurfacing pauses have been developed by the U.S. Navy from the work of the previously mentioned investigators.
Many gauges and computers have been designed for the purpose of aiding a SCUBA (self-contained underwater breathing apparatus) diver during a decompression ascent to avoid the bends. Probably the earliest and most comprehensive complex gauge is described in U.S. Pat. No. 3,457,393 to Stubbs and Kidd for an Analog Decompression Computing Device issued Jul. 22, 1969. This device employs mechanical gauges and sensors to gather and integrate data, for simulating the absorption of the inert gas component of air at changing pressures on human tissues, to assist a diver through decompression.
A subsequent device for computing a diver's decompression schedule is disclosed in U.S. Pat. No. 3,681,585 to Todd which issued Aug. 1, 1972. This device is basically an electronic device rather than mechanical as disclosed in the Stubbs and Kidd patent.
In the Sept. 1975 issue of Canadian Electronics Engineering, R. K. Lomnes described an electronic data processing device for SCUBA divers designed to prevent decompression sickness. The article was entitled "Microcomputers Applied to Underwater Diving" and the device disclosed in that article had the following features: the hardware included a real time (crystal-controlled) clock; an external analog pressure transducer; a digital to analog convertor; digital electronics; RAM and PROM memory; a microprocessor; a digital numeric liquid crystal display screen (LCD); and it was battery operated. This data processor permitted pre-dive planning; on-line dive monitoring; it used the Kidd-Stubbs four-tissue model for gas absorption; it displayed depth, total dive time, safe ascent depth, ascent time, and low battery indication. In addition, it was programmable to provide additional information to the diver. While the decompression calculator described in the article was a desktop device, an explicit reference was made to the future development of portable units for sports divers.
Subsequent to publication of the 1975 article, U.S. Pat. No. 4,192,001 was issued to Francesco Villa on Mar. 4, 1980, for A DECOMPRESSION ASCENT COMPUTER, which was essentially no different than the computer described in the 1975 article. Additional computers for use by SCUBA divers are disclosed in U.S. Pat. No. 3,992,948 to D' Antonio, et al. for DIVER INFORMATION SYSTEM, issued Nov. 23, 1976; U.S. Pat. No. 4,005,282 to Jennings for a DECOMETER issued Jan. 25, 1977; U.S. Pat. No. 4,054,783 to Seireg et al. for DECOMPRESSION PLAN DEVICE issued Oct. 18, 1977; and U.S. Pat. No. 4,109,140 to Etra for DIVER'S CONTROL AND INDICATION APPARATUS issued Aug. 22, 1978. None of these patents appear to teach anything novel over the 1975 article.
The purpose of each of the above-described computer devices is to aid a diver during decompression, i.e. during the period after they have exceeded the underwater time for a safe ascent without decompression.
One of the most serious concerns of a sport diver is to avoid the condition, caused by a combination of the time and depth he has been underwater, which requires a decompression ascent schedule for resurfacing. An important consideration for aiding a diver to avoid the problem is to present the complex information in a simple display rather than in numerical format which requires further interpretation or computation by the diver. Therefore, the present invention provides a computer which will integrate different sums of information and present it in a graphic display to aid a SCUBA diver in avoiding the necessity of a decompression ascent schedule.
The present invention is not a decompression meter as described by the previously referenced prior art. The invention continuously monitors air tank pressure, hydrostatic pressure, underwater time, and integrates that information between two formulas, using a different decompression model, to provide a graphic display which permits the SCUBA diver to avoid a decompression condition and monitor how close he comes to such a condition. It gives the diver all the information he needs to plan his dive, maintain a safe air reserve, and dive within the no-decompression limits accepted by the U.S. Navy.